The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.
Active noise cancellation (ANC) technology attempts to generate destructive interference sound waves to cancel out unwanted noise. ANC has been applied to numerous technologies such as headphones, communications systems, mechanical stability systems, heating ventilation and air conditioning (HVAC) systems and others with varying degrees of success. Recently, the concept of window mounted ANC devices which are tunable and which would provide a user the ability to selectivity eliminates outside noises have entered the market. Such window mounted ANC devices may use the windowpane as a speaker surface. For example, conceptually, a window mounted ANC may cause a window to vibrate in a pattern counter to the vibrations caused by the ambient noise, essentially turning the surface into a noise-canceling speaker. However, current window mounted ANC devices unsuccessfully attempt to use window vibrations to counter act vibrations made from static noise signals. Static noise signals refer to slowly changing and slowing evolving noise signals in reference to time. That is, the tones of the noises do not change quickly, but instead, maintain a steady frequency. For example, the hum of an air conditioning system, airplane engines flying overhead, or the noise generated from a loud server room are all examples of noises that are static.
Additionally, such window mounted ANC and other surface mounted ANC systems are unable to provide noise cancellation of dynamic noise signals. Dynamic noise signals are quickly varying, not auto-correlated, and/or non-periodic noise signals in time. Examples of dynamic noise signals include horns, sirens, dogs barking, people yelling, roosters crowing, and the like. Current ANC products are unable to provide cancellation of dynamic noise signals because dynamic noise signals are hard to track and/or to predict.
It would thus be advantageous to create an indoor ANC system that accounts for signals with dynamic frequency content. It would be advantageous to create such a system that employs transducer mounted to a surface that is capable of coupling noise. For example, the transducer may be mounted to windowpanes or walls capable of coupling noise. It would further be advantageous to provide such an ANC system that combines existing ANC technology with predictive techniques.